magnum or pre-magnum that is the ?

IF you are talking converting.....yes, Magnum is the best bolt on power adder. Caution...You do need provisions to oil through the push rods, and if your block is a hyd flat tappet you canNOT go with a hyd roller cam (like production magnums have). I'm converting an 87 360 to Magnum and found that info out. PLAIN Magnum heads are hard to find unless you have a donor or go with the R/T heads, Chrysler stopped making Magnum heads and are using the R/T heads on all the crate engines..trust me the price reflects it....
you should be able to bolt the 904 up to it though....